Method of separating the components of air



Dec. 30, 1947. c. c. VAN NUYS 2,433,536

HETHOD 0F SEPARATING THE COHPONENTS OF AIR Filed July 6, 1945 ?/a Ne H? Ne NVENTOR CAM V411 M/J BY .A/f? FROM M MAW; v P come/2s ATTORNEY Paiented Dec. 30, 1947 METHOD OF SEPARATING THE COM- PONENTS OF AIR Claude C. Van Nuys, Greenwich, Conn, assignor to Air Reduction Company, Incorporated, New York, N. Y., a corporation of New York Application July 6, 1945, Serial No. 603,555

7 Claims. i

This invention relates to the separation of the components of the atmosphere by liquefaction and rectification and particularly to the recovery of nitrogen and the components less volatile than nitrogen in a continuous operation. Neon and helium, which are more volatile than nitrogen, are not separated. Krypton and xenon are recovered as a single fraction substantially free from nitrogen, neon and helium. Oxygen and argon are separately recovered in substantial purity.

It is the object of the invention to provide a relatively simple and eflective procedure wherein air is subjected to successive operations to separate economically nitrogen, oxygen, argon and krypton-xenon free from nitrogen, neon and helium, each fraction being of commercial purity and suitable for the several uses for which they are respectively adapted.

Other objects and advantages of the invention will be apparent as it is better understood by reference to the followin specification and the accompanying drawing, which illustrates diagrammatically an apparatus suitable for the practiceof the invention, it being understood that details of the liquefaction system which are well known in the art are omitted in the interest of clarity.

In accordance with the invention, the air is first separated by liquefaction and rectification into two major components, a nitrogen effluent which includes the small amounts of neon and helium present in the atmosphere, and a liquid fraction consisting principally of oxygen and including argon and krypton-xenon. The liquid fraction is withdrawn and subjected to a second rectification with partial condensation of the effiuent to eliminate any nitrogen wh ch may have carried over with the liquid, to separate argon and to afford a liquid. fraction including oxygen and krypton-xenon. A third rectification of this liquid eliminates the krypton-xenon as a liquid,

of the auxiliary columns. The procedure as described can be conducted efiiciently without recompression of the gases. The air is initially compressed to some suitable pressure upward to 20 atmospheres absolute and cooled in the usual after-coolers. The successive operations thereafter are conducted at progressively lower pressures and produce continuously substantially pure nitrogen, oxygen and argon and the krypton-xenon mixture free from nitrogen, neon and helium.

Referring to the drawing, a column comprising sections 5 and 6 and an intermediate condenser section 1 i provided with trays 8 having the usual bubble caps 8a. The air from the after-coolers under suitable pressure is delivered from a pipe 9 through a flow regulating valve ill to a pipe I l and thence to a coil I2 in the bottom of the section 6 of the column. The air is liquefied by heat exchange with a pool of liquid which accumulates in the bottom of the column and is delivered through a pipe I3 and ,pressure reducing valve M to an intermediate level of the section 6. Flowing downwardly over the trays, the liquid becomes enriched in oxygen while vapors consisting of oxygen and, nitrogen rise through the tubes l5 of the condenser section I to a head Hi, The vapors are partially condensed, the oxygen flowing backwardly into the section 6 of the column. The residue, consisting principallyv of nitrogen, travels downwardly through the tubes I! in the condenser section I, and the resulting li u d accumulates in a collector l8. whence it isdelivered through a pipe 19 and pressure reducing valve '20 to the top of the section 5 of the column, thus affording the nitrogen reflux necessary to effective separation of oxy en from vapors arising through the section 5. Enriched oxygen liquid from the pool at the bottom of the section 6 of the column is delivered through a pipe 2| and valve 22 to a pipe 23 and thence to leaving substantially pure oxygen which escapes in the gaseous phase. In order to provide refrigeration for the two auxiliary rectiflcations and especially to restore to the main column the liquid equivalent of the liquid lost by that column through the pipe 22a, a portion of the air entering the system is initially separated to aiiord an enriched oxygen liquid which is delivered in an eflicient manner to the main rectifier to compensate that rectifier for its liquid loss above specified. The other portion of the air diverted to the auxiliary rectifier is uncondensed nitrogen of substantial purity. The latter is then liquefied and delivered to the condensers at the tops an intermediate level of the section 5 of the column. As the result of rectification of the two liquids in the section 5 of the column, nitrogen containing the small proportion of neon and helium present in the atmosphere escapes as an efiluent through a pipe 2| a at the top of the column and may be delivered through the usual exchangers (not shown) to suitable storage facilities.

The li uid which accumulates about the tubes l5 and I! in the condenser section 7 consist principally of oxygen but contains also argon and krypton-xenon. It is delivered through a pipe 22a and pressure reducing valve 23a to an intermediate level of a column 24 having the usual trays 25 and bubble caps 26, and flows downwardly over the trays. At the top of the auxiliary column 24, a condenser section 21 is provided with tubes 28 around which a pool of liquid nitrogen is maintained by means hereinafter described. The vapors rising through the tubes 28 are subjected to the cooling effect 'of the liquid nitrogen which condenses all of the vapors except any residual nitrogen which'may be present. The latter escapes through a pipe 29 controlled by a valve 30 and may be delivered to storage after passing through the usual exchangers (not shown) or discharged to the atmosphere. Directly beneath the condenser 21, the vapors rising through the auxiliary column 24 consist of substantially pure argon which iswithdrawn through a pipe 3| and delivered to storage. The liquid fraction which accumulates in the bottom of the auxiliary column 24 is oxygen including krypton-xenon. It surrounds a coil 32 in which nitrogen supplied as hereinafter described is' liquefied and delivered through a pipe 33 and pressure reducing valve 34 to'the condenser 21.

The liquid from the bottom of the auxiliary column 24 is delivered through a pipe 35 and flow regulating valve 36 to a second auxiliary column 31 having the usual trays 38 and bubble caps 38.

The liquid flows downwardly over the trays into a condenser section 48 having tubes 4| and is partially vaporized. The vapors rising through thetrays 38 pass upwardly through tubes 42 of a condenser section 43. The tubes are surrounded by liquid nitrogen withdrawn through an overflow pipe 44 in the condenser section 21 and delivered to the condenser section 43 through a pipe 45. Heat exchange with the cold nitrogen results in liquefaction of all but the oxygen present in the vapors. The latter escapes through a pipe 46 and after passing through the usual exchangers (not shown) may be delivered to storage. The vaporized nitrogen escapes through a pipe 41. The liquid which continuously flows downwardly over the trays 38 accumulates in the condenser section 40 and may be withdrawn from time to time through a pipe 48 controlled by a valve 49. 'This liquid is kryptonxenon free from nitrogen, neon and helium.

To provide the liquid nitrogen necessary for the separations accomplished in the two auxiliary columns, a portion of the entering high pressure air is withdrawn from the pipe 9 through a pipe 50 and delivered to the condenser section 40. It fiows upwardly through the tubes 4| in 'heat exchange relation with the liquid surround- 7 ing the tube and is partially condensed. The

The columns 24 and 31 will then be operated at fractions of an atmosphere below that maintained in the section 5 of the primary column. These pressures are, however, merely illustrative of suitable operation and may be varied without substantially modifying the results obtained.

The procedure affords large volumes of .relatively pure nitrogen. It can produce oxygen of any desired purity as for example from 95 to 99.6%, and both argon and krypton-xenon substantially free from nitrogen, neon and helium. As indicated, any nitrogen which may be carried over from the. primary column is eliminated in the first auxiliary column and hence cannot contaminate the argon, oxygen and kryptonxenon which are separated from the remaining liquid.

Various-changes may be made in the details of procedure as described without departing from the invention or sacrificing the advantages thereof.

I claim:

l. The method of recovering continuously from the atmosphere, nitrogen, oxygen, argon and krypton-xenon which comprises, initially separating air by liquefaction and rectification into a gaseous fraction consisting of a part of the nitrogen and air components more volatile than nitrogen and a liquid fraction consisting of the remaining components of air, separating nitrogen and argon respectively from the liquid fraction by rectification followed by partial condenliquid condensate is enriched oxygen liquid which is withdrawn through a pipe 5| and delivered through a pressure reducing valve 52 to the pipe 23 which conveys it with other enriched oxygen liquid into the section 5 of the primary column. The residue of the gas in the tubes 4| consists principally f nitrogen which is withdrawn through the pipe 53 and delivered to the coil 32 where it is liquefied as hereinbefore described; thus afiording the liquid refrigerating agent for the two auxiliary columns.

The procedure as described may be conducted at any suitable pressures sufiicient to ensure satisfactory operation. Thus, if the initial pressure is upward to 20 atmospheres, the pressure in the'section 6 of the primary column may be approximately 5 atmospheres absolute, and the pressure in the section 5 of the primary rectifier maybe approximately 1 atmosphere absolute.

sation of the effluent vapors from the rectification, and subjecting the residual liquid product of the second rectification to further rectification followed bypartial condensation of the effluent vapors from such further rectification to release oxygen in the vapor phase and to recover a liquid consisting essentiallyof krypton-xenon free from nitrogen, neon and helium.

2. The method of recovering continuously from the atmosphere, nitrogen, oxygen, argon and krypton-xenon which comprises, initially separating air by liquefaction and rectification into a gaseous fraction consisting of a part of the nitrogen and air components more volatile than nitrogen and a liquid fraction consisting of the remaining components of air, separating nitrogen arating air by liquefaction and rectification into a gaseous fraction consisting of a part of the nitrogen and air components more volatile than nitrogen and a liquid fraction consisting of the remaining components of air, separating nitrogen and argon respectively from the liquid .fraction by rectification followed by partial condensation of the efliuent vapors from the rectification by indirect heat exchange with liquid nitrogen, subjecting the residual liquid to further rectification followed by partial condensation of the effluent vapors from such further rectification to release oxygen in the vapor phase and to recover a liquid consisting essentially of krypton-xenon free from nitrogen, neon and helium, and providing the liquid nitrogen by partial condensation of a portion of the air undergoing treatment and condensation of the residual nitrogen.

4. The method of recovering continuously from the atmosphere, nitrogen, oxygen, argon and krypton-xenon which comprises, initially separating air by liquefaction and rectification into a gaseous fraction consisting of a part of the nitrogen and air components more volatile than nitrogen and a liquid fraction consisting of the remaining components of air, separating nitrogen and argon respectively from the liquid fraction by rectification followed by partial condensation of the effluent vapors from the rectification by indirect heat exchange with liquid nitrogen, subjecting the residual liquid to further rectification followed by partial condensation of the efliuent vapors from such further rectification to release oxygen in the vapor phase and to recover a liquid consisting essentially of kryptonxenon free from nitrogen, neon and helium, and providing the liquid nitrogen by directing a portion of the air undergoing separation in indirect heat exchange with the krypton-xenon liquid to effect partial condensation of the air and conducting the uncondensed residue in indirect heat exchange with the liquid oxygen fraction.

5. The method of recovering continuously from the atmosphere, nitrogen, oxygen, argon and krypton-xenon which comprises, initially separating air by liquefaction and rectification into a gaseous fraction consisting of a part of the nitrogen and air components more volatile than nitrogen and a liquid fraction consisting of the remaining components of air, separating nitrogen and argonrespectively from the liquid fraction by rectification followed by partial condensation of the efliuent vapors from the rectification by indirect heat exchange with liquid nitrogen, and subjecting the residual liquid to further rectification followed by partial condensation of the eiiluent vapors from such further rectification by indirect heat exchange with liquid nitrogen to release oxygen in the vapor phase and to recover a liquid consisting essentially of krypton-xenon free from nitrogen, neon and helium.

6. The method of recovering continuously from the atmosphere, nitrogen, oxygen, argon and krypton-xenon which comprises, initially separating air by liquefaction and rectification into a gaseous fraction consisting of a part of the nitrogen and air components more volatile than nitrogen and a liquid fraction consisting nitrogen by partial condensation of a portion ofthe air undergoing treatment and condensation of the residual nitrogen.

7. The method of recovering continuously from the atmosphere, nitrogen, oxygen, argon and krypton-xenon which comprises, initially separating air by liquefaction and rectification into a gaseous fraction consisting of a part of the nitrogen and air components more volatile than nitrogen and a liquid fractionconsisting of the remaining components of air, separating nitrogen and argon respectively from the liquid fraction by rectification followed by partial condensation of the efiiuent vapors from the rectification by indirect heat exchange with liquid nitrogen, subjecting the residual liquid to further rectification followed by partial condensation of the eiiiuent vapors from such further rectification by indirect heat exchange relation with liquid nitrogen to release oxygen in the vapor phase and to recover a liquid consisting essentially of krypton-xenon free from nitrogen,

neon and helium, and providing the liquid nitrogen by directing a portion of the air undergoing separation in indirect heat exchange with the krypton-xenon liquid to effect partial condensation of the air and conducting the uncondensed residue in indirect heat exchange with the liquid oxygen fraction.

CLAUDE c. VAN NUYS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,051,576 Schlitt Aug. 18, 1936 2,146,197 Twomey Feb. 7, 1939 OTHER REFERENCES Book, The Separation of Gases by Ruhemann,

published by Oxford Uni. Press. (A copy of this book is in Div. 44 of the Patent Oflice.) 

